“You ain’t seen nothin’ yet,” or so says the marketing campaign for “Jolson,” lifting one of the singer’s most celebrated lines. In West End terms, the quote just might be apt. In these unfortunate times of “Fame, the Musical” and “The Fields of Ambrosia,” “Jolson” is that rare big-budget London show to have a professional sheen to it without involving either Andrew Lloyd Webber or Cameron Mackintosh. Does “professional” mean good? That is another question audiences may be left pondering when they ask why a show put together with such obvious affection is also so dull.

The musical faces the same dilemma that has always bedeviled “Mack and Mabel, ” “Jolson’s” main competitor in the upcoming Olivier Awards: How do you put an egotist at center stage? The real Al Jolson — a.k.a. Asa Yoelson, the Lithuania-born cantor’s son — had an astonishing career encompassing minstrel shows, vaudeville, Brodway and Hollywood between the teens and 1940s, the decades covered in “Jolson.” But his relationship with second wife Ruby Keeler (Sally Ann Triplett), whom he married in 1928, was one of several that were more turbulent than “Jolson” chooses to suggest. As warts-and-all biographies go, this one is barely a pimple.

And what of the blacking-up past of a performer who once billed himself “the blackface with the grand opera voice”? Mindful of our PC age, “Jolson” gets that out of the way as swiftly and guiltily as possible, going so far as to script a scene in which a motherless young black boy, Sammy (Timothy Walker), sings for Brian Conley’s Jolson and gets cash and a hug in return. It’s up for grabs which is more offensive — skating over the potentially controversial parts of a life or apologizing for them via revisionist sentimentality.

The “Jolson” team — director Rob Bettinson included — spawned “Buddy,” and this show follows the Buddy Holly-biotuner formula, spruced up with lavish sets from Robert Jones that never reach the “Crazy for You” level to which they seem to aspire. (Ditto Tudor Davies’ choreography, which could use a dollop of Susan Stroman-style wit.)

The book by Francis Essex and Rob Bettinson is heftier than that for “Buddy,” but in the end no less perfunctory. Both display the creators’ itch to abandon biography and cut to the concert. “Jolson,” accordingly, ends with a vocal display from Conley that whips up the audience in a way that the predictable parade of agents (a nicely avuncular John Bennett as Al’s longtime agent Louis Epstein), producers (Brian Greene’s Lee Shubert among them) and lovers and wives never does. And lest “The Jolson Story” go unmentioned, a film clip is dutifully shown through which Conley bursts as Larry Parks finishes “My Mammy,” Radio City drops from the wings, and our very own Jolson wannabe rips into “Swanee.”

Conley — a TV star and West End alum of “Me and My Girl” — has generated the show’s greatest buzz. and it’s true that the burly performer (he’d make a great Mack Sennett) gets Jolson’s back-of-the-throat, near-bark of a voice, even if all one need do is listen to the real Jolson on the closing credits of the Ian McKellen film “Richard III” to hear a richness of timbre Conley doesn’t possess; he’s a shade metallic. In the end, one’s left admiring the hard work behind the performance without particularly warning to it. Pretty much the same could be said of the show.

Jolson

Production

LONDON A Paul Elliott, Laurie Mansfield and Greg Smith for the Jolson Company Ltd. presentation, in association with Chas. Elliott, of a Theater Royal Plymouth production of a musical in two acts, written by Francis Essex and Rob Bettinson from an original idea by Michael Freedland. Directed by Bettinson,